Fuel filter

ABSTRACT

The present invention relates to a fuel filter ( 1 ) for a fuel supply system of an internal combustion engine, in particular in a motor vehicle, comprising a filter housing ( 2 ) and a filter element ( 3 ). The filter housing ( 2 ) has an untreated-side inlet ( 4 ), a treated-side outlet ( 5 ) and an untreated-side return line ( 6 ). The filter element ( 3 ) is arranged in the filter housing ( 2 ) and, therein, separates an untreated space ( 13 ), which communicates with the inlet ( 4 ) and with the return line ( 6 ), from a treated space which communicates with the outlet ( 5 ). Additionally provided is a closure element ( 20 ) which, in the operationally ready state of the fuel filter ( 1 ), closes off the return line ( 6 ).

The present invention relates to a fuel filter for a fuel supply systemof an internal combustion engine, in particular in a motor vehicle.

Internal combustion engines have a fuel supply system for their supplywith liquid fuel. Such a fuel supply system comprises typically a fueltank, a fuel pump, a fuel filter, and an injection system. To reduce therisk of damage of the injection system or the internal combustionengine, respectively, it is required to clean the fuel supplied to theinternal combustion engine from contamination carried along with thefuel. Hence, the fuel filter is a component which is relevant for thefunctional reliability of the internal combustion engine. Such a fuelfilter has typically a filter housing which comprises an untreated-sideinlet and a treated-side outlet. Furthermore, a filter element isprovided, which is arranged in the filter housing and which separates inthe filter housing an untreated space communicating with the inlet froma treated space communicating with the outlet. The filter element is awear part which is replaced in certain maintenance intervals. Whenreplacing the filter element, there is a risk that it is not properlyinstalled in the filter housing. Moreover, there is a risk that the fuelfilter is operated, accidentally or knowingly, without filter element.With missing or improper installed filter element, there is the riskthat contamination can get unhindered to the injection system or to theinternal combustion engine, respectively.

The present invention is concerned with the problem to propose animproved embodiment for a fuel filter, for which in particular the riskis reduced that unfiltered fuel can get to the internal combustionengine.

This problem is solved in the invention by means of the subject mattersof the independent claims. Advantageous embodiments are subject matterof the dependent claims.

The invention is based on the general idea to in addition provide thefuel filter with an untreated-side return line, which, in theoperationally ready state, is closed by means of a closure element. Inan inoperable state of the fuel filter, thus, for example, with missingclosure element and/or missing filter element, the return line is open,so that fuel supplied through the inlet into the filter housingpreferably flows off through the return line and, for example, flowsback into the fuel tank. In this case, no, or not enough, fuel issupplied. Subsequently, the internal combustion engine cannot bestarted. The risk of damage of the injection system, or the internalcombustion engine, respectively, can thereby be reduced. To ensure thatwith missing filter element, the fuel entering the filter housing exitsthrough the return line and not through the outlet, the flow resistancethrough the return line to the tank, for example, can be ratedconsiderably lower than the flow resistance from the outlet to theinternal combustion engine. With inserted filter element and withmissing or improper attached closure element, the return line to theuntreated space is open, while the outlet towards the treated space isopen and is separated by the filter element from the untreated space. Bymeans of the filter element, an increased flow resistance is forced tooccur towards the outlet. Accordingly, also in this constellation, thefuel discharges through the return line from the filter housing. In thisconstellation, the filter element subsequently prevents the supply ofcontamination to the internal combustion engine, whereby the same cannotbe started at the same time, since it is not supplied, or onlyinsufficiently, with fuel through the outlet.

In a preferred embodiment, the closure element is formed or arranged atthe filter element such that the closure element, with a filter elementproperly inserted into the filter housing, closes off the return line.By means of this integrated construction, it is ensured that the returnline is closed off only with inserted, and correctly inserted, filterelement. In other words, the proper installation state of the filterelement, or the operationally ready state of the fuel filter,respectively, is only given when the filter element is inserted into thefilter housing such that the closure element closes off the return line.The reliability or the handling of the fuel filter is thereby improved.

In another embodiment, a positioning device can be provided, whichcomprises at least one positioning element on the filter element side,and one positioning element on the filter housing side, which interactduring inserting of the filter element into the housing for finding ofan orientation, which is aligned with the insertion direction of theclosure element shaped as a pin, between the pin and a return lineopening, which is open towards the untreated space, of the return line.By means of this design, during mounting of the fuel filter, the findingof the relative position between filter element and filter housing ismade easier. The risk of a faulty installation is thereby reduced.

In another advantageous embodiment, a guiding device can be provided,which comprises at least one guiding element on the filter element side,and at least one guiding element on the filter housing side, whichinteract during insertion of the filter element into the filter housingaccording to the key-lock principle, such that they allow theinteracting between the positioning elements of the positioning deviceonly with matching guiding elements. By means of this construction, therisk is reduced that a wrong filter element, thus a filter element,which is not specifically adapted to the fuel filter, can be insertedinto the filter housing. In the ideal case, an internal combustionengine, the fuel supply system of which is equipped with the fuel filteraccording to the invention, can be started only when the associated andcorrect filter element is properly inserted into filter housing.

Further important features are apparent from the sub-claims, from thedrawings, and from the associated description of the figures by means ofthe drawings.

It is to be understood the aforementioned and the following featuresstill to be illustrated are not only usable in the respective mentionedcombination, but also in other combinations or on its own, withoutdeparting from the scope of the present invention.

Preferred exemplary embodiments of the invention are illustrated in thedrawings, and are explained in the following description in more detail,wherein identical reference numbers refer to identical, or similar, orfunctionally identical components.

In the figures

FIG. 1 shows schematically a perspective and partial cross section of afuel filter,

FIG. 2 shows schematically a partial cross section and a greatlysimplified side view in the region of a return line during installationof a filter element,

FIG. 3 shows schematically a perspective view on a cover of the filterhousing in a simplified illustration,

FIG. 4 shows a top view on the cover according to FIG. 3 correspondingto an arrow IV in FIG. 3,

FIG. 5 shows a view as in FIG. 4, but for a different embodiment,

FIG. 6 shows schematically a detail section along the section lines VIin FIG. 4.

According to FIG. 1, a fuel filter 1, which is suitable for filtering aliquid fuel, such as, e.g., gasoline or diesel, comprises a filterhousing 2 and a filter element 3. The filter housing 2 comprises anuntreated-side inlet 4, a treated-side outlet 5, and an untreated-sidereturn line 6. The filter housing 2 is assembled from a cup-shaped cover7 and a cup-shaped bottom 8, which can be screwed together by means of athreaded connection 9. Inlet 4, outlet 5 and return line 6 are formedhere at the cover 7. The filter housing 2 is preferably provided for ahanging mounting position so that for maintenance of the fuel filter 1,the bottom 8 can be screwed off downwards, while the upper cover 7remains stationary. Alternatively, a standing mounting position can alsobe provided, whereby then the cover 7 comprising the connections 4, 5,and 6 is arranged at the bottom, remains stationary, and functionallyforms rather a “housing bottom”, while in this mounting situation thebottom 8 is arranged at the top, and functionally rather forms a“housing cover”. The axial dimension can vary here. In particular, inthe standing arrangement, the cover 7, thus the functional housingbottom, can accommodate the bigger portion of the filter element 3,while in the shown hanging arrangement, the bottom 8 accommodates thebigger portion of the filter element 3.

The fuel filter 1 is provided for mounting into a fuel supply system ofan internal combustion engine, which is preferably arranged in a motorvehicle. For this, the inlet 4 can be connected to an inlet line 10,symbolized by an arrow, of the fuel supply system, the outlet 5 to anoutlet line 11, symbolized by an arrow, of the fuel supply system, andthe return line 6 to a return pipe 12, symbolized by an arrow, of thefuel supply system. The inlet line 10 includes, for example, a fuelpump, and comes from a fuel tank. The outlet line 11 runs, for example,to a fuel injection system. The return pipe 12 runs preferably back tothe fuel tank.

The filter element 3 is arranged in the mounted state of the fuel filter1 in the filter housing 2 such that it separates within the filterhousing 2 an untreated space 13 from a treated space 14. In the shownexemplary embodiment, the filter element 3, without restriction of thegenerality, is shaped as ring filter element, which, with respect to alongitudinal center axis 15 of the ring filter element 3, is arrangedcoaxial to a longitudinal center axis 16 of the filter housing 2.Furthermore, the ring filter element 3 includes at least one axial enddisk 17, wherein in FIG. 1 only one end disk is visible. The respectiveend disk 17 borders axially a filter material 18 which allows a radialflow-through.

The inlet 4 communicates via an inlet opening, not shown here, with theuntreated space 13, and the outlet 5 communicates via an outlet opening,not shown, with the treated space 14. Furthermore, the return line 6communicates with the untreated space 13 as well. For this, the returnline 6 includes, for example, a return line opening 19, which is opentowards the untreated space 13.

For the fuel filter 1, in addition, a closure element 20 is providedwhich serves for closing off the return line 6 in the operationallyready state of the fuel filter 1. Here, the closure element 20 closesoff, for example, the return line opening 19. In the operationally readystate of the fuel filter 1, hence with closed return line 6, the fuelpump supplies, during the operation of the fuel supply system, fuelthrough the inlet 4 into the untreated space 13. From the untreatedspace 13, the fuel gets through the filter material 18 radially to thetreated space 14. From the treated space 14, the fuel discharges againthrough the outlet 5 from the filter housing 2. With missing closureelement 20, or when the return line 6 is not closed off by the closureelement 20, respectively, the fuel from the untreated space 13 can exitdirectly through the return line 6 out of the filter housing 2. The flowresistance through the filter material 18 to the treated side 14 herebyprovides that within the treated space, thus at the outlet 5, therequired fuel pressure for starting the internal combustion enginecannot be built up since the fuel from the untreated space 13 candischarge substantially unrestricted through the return line 6.

In the preferred embodiment shown here, the fuel filter 1 can inaddition be equipped with a pressure sensor 21, by means of which thetreated fuel pressure can be measured. The pressure sensor 21 isattached, for example, at the cover 7. For example, when starting theinternal combustion engine, an engine control device can monitor thepressure build-up in the treated space, and generates the respectivestart signals for starting the internal combustion engine only at asufficient pressure build-up. With a closed return line 6, the hererequired pressure in the treated space cannot build up, so that thenecessary start signals are not generated. Besides, with an open returnline 6, the pressure build-up in the treaded space can turn out so lowthat the required fuel supply for starting the internal combustionengine is not possible, so that the internal combustion engine cannot bestarted due to the insufficient or missing fuel supply. Thisconstruction is based on the idea that the unclosed return line isevaluated as an indication that the closure element 20 is not, or notproperly, inserted into the return line opening 19, and/or that thefilter element 3 is not, or not properly, inserted into the filterhousing 2. The unclosed return line 6 can also indicate that a wrongfilter element was inserted into the filter housing 2. In the mentionedstates, the fuel filter 1 is not operationally ready. The internalcombustion engine should then not be started to avoid damage of theinternal combustion engine, or the injection system, respectively, byunfiltered fuel. By means of the proposed fuel filter 1, this goal isachieved comparatively easily and effectively.

In the preferred embodiment shown here, the closure element 20 is formedat the filter element 3, or is arranged thereon, respectively. Thus, thereturn line 6 is automatically closed off when the filter element 3 isinserted properly into the filter housing 2. A missing filter element 3,a wrongly inserted filter element, and the use of a wrong filter element3 result in each case in an unclosed return line 6, whereby the startingof the internal combustion engine can be prevented.

In the example, the closure element 20 is arranged at the end disk 17facing towards the cover 7. The closure element 20 is shaped here as pin22, which projects axially from the end disk 17, thus parallel to thelongitudinal center axis 15 of the ring filter element 3. The pin 22interacts with the return line opening 19 for closing off the returnline 6. In particular, the pin 22 can be plugged in axially into thereturn line opening 19. The pin 22 can be equipped with a radial seal23, in particular with an O-ring. The return line opening 19 can beequipped with a fitting or a tube section, which are not described herein more detail. In the plugged-in state, the radial seal 23 causes asufficient sealing of the return line opening 19.

In the embodiment shown here, the fuel filter 1 is additionally equippedwith a vent throttle 24, through which the return line 6 alsocommunicates with the untreated space 13. The vent throttle 24 ischaracterized by a flow-through resistance, which is substantiallyhigher than the flow-through resistance of the filter element 3 and theoutlet 5 with closed-off return line 6. With closed-off return line 6,the vent throttle 24 allows a ventilation of the filter housing 2 duringstarting of the internal combustion engine. In the subsequent normaloperation, it allows a comparatively small return flow through thereturn line 6, which, however, due to the comparatively strong throttleeffect of the vent throttle 24, does not hinder the required pressurebuild up in the treated space 14. In particular, the flow-throughresistance of the vent throttle 24 is even higher than the flow-throughresistance of the filter element 3 alone.

For a standing arrangement, a different, in particular higher,positioning of the vent throttle is thinkable. In the standing position,the return line 6, which is then arranged at the bottom, can serve asidle, which, at removal of the bottom 8 located at the top, or atpulling out of the filter element 3, opens up automatically.

According to FIG. 2, the fuel filter 1 can be equipped with apositioning device 25. The positioning device 25 comprises on the filterelement side at least one position element, which is formed here by aslide face 26 at the free end of the pin 22, and, on the filter housingside, at least one positioning element, which is formed here by a ramp27. The positioning elements 26, 27 are shaped such that they interactduring placing of the filter element 3 into the filter housing 2 forfinding of an orientation, which is aligned with the insertion directionof the pin 22, between the pin 22 and the return line opening 19.

In the preferred embodiments shown here, as a positioning element on thefilter housing side, the said ramp 27 is provided, which projectsaxially into the untreated space 13. The ramp 27 begins at 29 at thereturn line opening 19 and ends at 30 at the return line opening 19 aswell. Between its beginning 29 and its end 30, the ramp 27 extendscircular or helical, respectively, concentric to the longitudinal centeraxis 16 of the filter housing. From its beginning 29 to its end 30, theramp 27 declines towards the return line opening 19. The said slide face26 is formed at the pin 22 as a position element on the filter elementside, in fact on a side of the pin 22 remote from the end disk 17. Here,the pin 22 is arranged eccentrically with respect to the longitudinalcenter axis 15 of the filter element 3, wherein the eccentricity of thepin 22 is selected approximately equal to the radius of the ramp 27.Accordingly, the pin 22 can rest with its slide face 26 axially againstthe ramp 27 during insertion of the filter element 3, coaxial to thelongitudinal center axis 16 of the filter housing 2. During turning ofthe filter element 3 around its longitudinal center axis 15corresponding to an arrow 31, the pin 22 slides with its slide face 26along the ramp 27. Hereby, the orientation of the pin 22 is forced tooccur towards the return line opening 19. A corresponding slidingmovement is symbolized in FIG. 2 by an arrow 32. The orientation of theramp slope is preferably selected such that the turning direction duringtightening of the bottom 8 is forced to generate the desired turningdirection 31 for the filter element 3 arranged therein, whereby thefilter element 3 during attaching of the bottom 8 automatically slidesalong the ramp 27. Upon obtaining the aligned orientation between pin 22and the return line opening 19, the beginning 29 of the ramp 27restricts a further turning of the filter element 3. With furthertightening of the bottom 8, the filter element 3 is forced to beinserted corresponding to the insertion direction 28 with its pin 22into the return line opening 19.

According to FIGS. 3 to 6, the fuel filter 1 can additionally beequipped with a guiding device 33. This guiding device 33 can compriseon the filter element side at least one guiding element, which, forexample, can be formed by a guiding section 34 formed at the pin 22, aswell as on the filter housing side at least one guiding element, which,for example, can be formed by one or more guiding walls 35. The guidingelements 34, 35 are shaped such that they interact during insertion ofthe filter element 3 into the filter housing 2 according to the“key-lock principle”. This means that the guiding elements 34, 35 allowinteracting between the positioning elements 26, 27, thus between theramp 27 and the slide face 26, only when the matching guiding elements34, 35 interact with each other. In the case that the guiding elements34, 35 interacting with each other during insertion of the filterelement 3 into the filter housing 2 do not match, the interacting of thepositioning elements 26, 27 for finding the aligned orientation betweenthe pin 22 and the return line opening 19, is considerably hindered ormade impossible by the guiding device 33.

In the shown embodiment, the guiding elements on the filter housing sideare formed by guiding walls 35 which extend radially inside and/orradially outside along at least one extension section 36 of the ramp 27,thereby projecting beyond the ramp 27 in axial direction. In each of theexamples of FIGS. 3 and 4, respectively, only one extension section 36is provided, which is positioned in the region of the end 30 of the ramp27. Here, in the extension section 36, two parallel guiding walls 35 areprovided, one of which borders the ramp 27 radially inside and the otherone radially outside. In the embodiment shown in FIG. 5, a total ofthree extension sections 36 are provided, in each of which two parallelextending guiding walls 35 are provided, which border the ramp 27radially inside and outside. The guiding element on the filter elementside of the embodiments shown here is formed by the guiding section 34,which projects axially on the side of the pin 22, which is facing awayor is remote from the end disk 17. The said guiding section 34 comprisesthe slide face 26 of the pin 22. Furthermore, the guiding section 34 isadjusted with respect to its positioning at the pin 22 and with respectto its dimensioning to the guiding walls 35 such that the guidingsection 34, during installation of the fuel filter 1, extends radiallyalongside the respective guiding wall 35 or between the two parallelguiding walls 35, respectively, thereby resting with the slide face 26axially against the ramp 27 and keeping the pin 22 axially spaced apartfrom the respective guiding wall 35. This relationship is particularlyapparent in FIG. 6. There, the guiding section 34 contacts the ramp 27running between the guiding walls 35 with the slide face 26, and ensuresan axial clearance between the walls 35 and an outer side 37, facingaway from or remote from the end disk 17, of the pin 22, and from whichthe guiding section 34 projects. The said outer side 37 can be plane andcan merge via a chamfer 38 into the rest of the pin 22.

The above mentioned key-lock principle now causes that the pin 22 withits slide face 26 can slide along the entire ramp 27 only until thealigned orientation to the return line opening 19 when the guidingsection 34 is present, when the guiding section 34 is sufficientlynarrow in radial direction to fit through the opposing guiding walls 35,and when the guiding section 35 is sufficiently long in axial directionto adjust the required axial clearance between pin 22 and the guidingwalls 35. With missing or wrong guiding section 34, the pin 22 wouldrest against the face ends of the walls 35 when sliding along the ramp27 in circumferential direction, whereby the turnability of the filterelement 3 is blocked. Then, the filter element 3 cannot be readilyinstalled properly.

In the FIGS. 3 to 6, in addition an outlet fitting 39 is illustrated,which is provided at the cover 7 and onto which the filter element canbe slipped. FIG. 6 shows a special embodiment in which the pin 22 isattached through a web 40 to the end disk 17. Said web 40 is flexible inradial direction and allows a tolerance compensation between the radialposition of the guiding section 34 and the radial position of theguiding walls 35. As is apparent from FIG. 1, the pin 22 also can beattached comparatively rigid to the end disk 17.

1. A fuel filter for an fuel supply system of an internal combustionengine, comprising: a filter housing, which has an untreated-side inlet,a treated-side outlet and an untreated-side return line, a filterelement which is arranged in the filter housing, the filter elementincluding an untreated space and a treated space, and which separates inthe filter housing the untreated space communicating with an inlet andthe return line from the treated space communicating with the outlet, aclosure element which in an operationally ready state of the fuel filtercloses-off the return line.
 2. The fuel filter according to claim 1,wherein the closure element is one of formed and arranged at the filterelement, and, with the filter element inserted into the filter housing,closes-off the return line.
 3. The fuel filter according to claim 1,wherein the closure element is arranged at an end disk of the filterelement shaped as ring filter element having at least one axial enddisk.
 4. The fuel filter according to claim 3, wherein the closureelement is shaped as a pin which projects axially from the respectiveend disk, and which, for closing the return line, closes-off a returnline opening, which connects the return line with the untreated space.5. The fuel filter according to claim 1, wherein a positioning device isprovided which comprises at least one positioning element on a filterelement side, and at least one positioning element on a filter housingside, which interact during insertion of the filter element into thefilter housing for finding of an orientation, which is aligned with aninsertion direction of the closure element shaped as a pin, between thepin and a return line opening, which is open towards the untreatedspace, of the return line.
 6. The fuel filter according to claim 4,wherein the filter housing comprises a ramp which projects into theuntreated space, which begins at the return line opening, extendscircular concentric to a longitudinal center axis of the filter housing,ends at the return line opening, and declines from a beginning of theramp to an end of the ramp towards the return line opening, and that thepin is arranged eccentric to a longitudinal center axis of the filterelement and comprises a slide face which slides along the ramp duringturning of the filter element around the longitudinal center axis of thefilter housing for orienting the pin towards the return line opening. 7.The fuel filter according to claim 6, wherein a guiding device isprovided which comprises at least one guiding element on the filterelement side, and at least one guiding element on the filter housingside, which interact during insertion of the filter element into thefilter housing according to a key-lock principle such that the at leastone guiding element on the filter element side and the at least oneguiding element of the filter housing side allow for at least one of thefollowing: interacting between the slide face and the ramp andinteracting between the ramp and the slide face only in case the atleast one guiding element on the filter element side matches the atleast one guiding element on the filter hosing side.
 8. The fuel filteraccording to claim 7, wherein the ramp along one of an entire extensionof the ramp, and at least along an extension section of the ramp, isbordered at least one of radially inside and radially outside by atleast one guiding wall which projects axially beyond the ramp, and thatthe pin comprises an axially projecting guiding section which comprisesthe slide face and which is positioned and dimensioned such that the pinextends radially alongside the respective guiding wall and thereby reststhe slide face axially against the ramp, and keeps the pin axiallyspaced apart from the respective guiding wall.
 9. The fuel filteraccording to claim 1, wherein the return line in addition communicateswith the untreated space through a vent throttle, the flow-throughresistance of which is higher than the flow-through resistance throughthe filter element and through the outlet at the return line that isclosed off.
 10. The fuel filter according to claim 1, wherein a pressuresensor is provided for measuring a treated-side fuel pressure.
 11. Thefuel filter according to claim 1, wherein the filter element is shapedas a ring filter element, and comprises at least one axial end disk,from which a closure element projects axially and eccentrically, and afilter element is inserted into a filter housing of the fuel filter,closes-off an untreated-side return line of the filter housing.
 12. Thefuel filter according to claim 11, wherein the closure element is a pin.13. The fuel filter according to claim 2, wherein the closure element isarranged at an end disk of the filter element shaped as ring filterelement having at least one axial end disk.
 14. The fuel filteraccording to claim 2, wherein a positioning device is provided whichcomprises at least one positioning element on a filter element side, andat least one positioning element on a filter housing side, whichinteract during insertion of the filter element into the filter housingfor finding of an orientation, which is aligned with an insertiondirection of the closure element shaped as a pin, between the pin and areturn line opening, which is open towards the untreated space, of thereturn line.
 15. The fuel filter according to claim 2, wherein thereturn line in addition communicates with the untreated space through avent throttle, the flow-through resistance of which is higher than theflow-through resistance through the filter element and through theoutlet at the return line that is closed off.
 16. The fuel filteraccording to claim 2, wherein a pressure sensor is provided formeasuring a treated-side fuel pressure.
 17. The fuel filter according toclaim 2, wherein the filter element is shaped as a ring filter element,and comprises at least one axial end disk, from which a closure elementprojects axially and eccentrically, and a filter element is insertedinto a filter housing of the fuel filter, closes-off an untreated-sidereturn line of the filter housing.
 18. The fuel filter according toclaim 3, wherein the return line in addition communicates with theuntreated space through a vent throttle, the flow-through resistance ofwhich is higher than the flow-through resistance through the filterelement and through the outlet at the return line that is closed off.19. The fuel filter according to claim 3, wherein a pressure sensor isprovided for measuring a treated-side fuel pressure.
 20. The fuel filteraccording to claim 3, wherein the filter element is shaped as a ringfilter element, and comprises at least one axial end disk, from which aclosure element projects axially and eccentrically, and a filter elementis inserted into a filter housing of the fuel filter, closes-off anuntreated-side return line of the filter housing.